(sonicArts) delays and resonators

Audio delay is a simple process that allows for a variety of audio effects.

In the most basic implementation, incoming audio is copied. The copy is delayed by some some specified time and its amplitude is scaled before mixing it back into the original signal. Short delay times – generally less than 20 ms – can produce a filtered effect. Longer delay times produce discrete echoes.

Taking the mixed, original and delayed signal, and returning it to the original audio signal before delay is applied is called feedback. Here is a simple diagram of a delay line. (The bypass factor is the same as the Dry/Wet mix.)


The feedback signal must have its amplitude scaled to a factor of less than 1 or the signal will gain in amplitude rather quickly to an uncomfortable level.

Discrete echoes can be used as part of a reverberation effect, to create thickness, or as a special effect. Couple longer delay times with feedback amplitudes of .5 (50%) or below.

Short time delays with high feedback amplitudes can create resonator effects, causing amplification of a frequency component found in the input. Ableton Live and Cecilia (both versions 4 and 5) offer excellent examples. The feedback amplitude usually needs to be above .9 for any resonator effect to be heard, and is most effective when it is very close (but still below) 1. I typically use feedback amplitudes above .99 for best effect. At these feedback amplitudes you need to be very careful about amplitude in and out of the delay effect, as the feedback will be adding a significant amount of gain to the original input.

Most resonator effects allow you to specify the pitch you want resonated, setting the delay time accordingly. But you can easily figure out how to set a delay time for any given pitch by finding the period of the fundamental frequency in milliseconds.

To find the period in seconds you would divide 1 by the frequency. To find the period in milliseconds, which is the unit used for most delay effects, you would divide 1000 by the frequency.

In basic steps:

  1. Specify the pitch you want to resonate (C4, for example, or MIDI note number 60).
  2. Convert the pitch to frequency (C4 is approximately 261 Hz).
  3. Divide 1000 ms (1 second) by the frequency to get the delay time to resonate that frequency (1000/261 = approx 3.8 ms)


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